The present invention relates generally to motor vehicles and, more particularly, to a uniquely configured steering mechanism which may be adapted for use on the front wheel of a motorcycle and which is specifically adapted to minimize the amount of dive experienced by the front end of the motorcycle during braking but which also allows for self-centering of the wheel due to a forward location of a virtual steering axis ahead of the wheel centerline.
Prior art front suspension systems for motorcycles are universally fitted with a pair of telescopic front forks which are attached to a front end of the motorcycle at the steering stem and which have the front wheel mounted to the lower ends of the front forks. The telescopic forks typically include a suspension and damping system for absorbing road shocks transmitted through the telescopic forks via compression springs which also accommodate variations in motorcycle and rider weight. The telescopic forks typically further include a damping mechanism in order to provide a dampening effect against oscillations induced in the compression springs responding to surface irregularities.
The telescopic front forks employed by a majority of motorcycles are pivotable through the use of handlebars by which the rider maintains steering control of the motorcycle. The handlebars typically include additional rider controls such as a throttle for regulating engine speed, a front brake lever for reducing rotational speed of the front wheel, and a clutch lever to selectively engage and disengage the engine from the motorcycle transmission. Various other rider controls may be incorporated into the handlebars including, but not limited to, an engine kill switch, turn signal controls, and headlight controls.
Although the telescopic front fork system has been successfully incorporated into a majority of motorcycles produced up to the present, conventional telescopic forks suffer from several deficiencies which detract from their overall utility. For example, because the front wheel is essentially cantilevered outwardly from the front end of the motorcycle at a relatively long distance from the front end, the front forks themselves as well as the steering head and the motorcycle frame attach points for supporting the steering head must have a sufficiently high cross sectional moment of inertia in order to provide the necessary rigidity and resistance to flexure of the motorcycle frame in response to road shocks.
The high degree of stiffness in the front forks and the motorcycle frame is especially important when the motorcycle is driven at high speeds in order to avoid the development of wobble at the front wheel which can occur as a result of lateral flex in the fork legs allowing the tire contact patch to move away from the steering axis. The ability to resist undue flexing unfortunately results in an increase in weight of the front forks and motorcycle frame. To complicate the matter, heavy front forks generate high inertia in the steering system which results in a steering system that is even more prone to wobble.
Another disadvantage associated with the front telescopic forks of conventional motorcycles is that the point of the steering stem where the front forks are connected to the motorcycle frame is positioned substantially above the motorcycle center of gravity. The relatively high connection point of the front forks further raises the center of gravity which has the unfortunate effect of reducing handling performance of the motorcycle and especially during low-speed maneuvering or when the motorcycle is at rest and supported only by the rider.
A further drawback associated with conventional telescopic forks of the prior art is related to the tendency of the front end of the motorcycle to dive under heavy braking as the weight of the motorcycle is transferred to the front wheel. During front-end dive, the compression springs in the front forks are further compressed which reduces the ability of the compression springs to absorb and dissipate irregularities or bumps in the road during braking. In extreme cases, the phenomena of front-end dive presents a safety issue as the motorcycle can potentially flip forward under severe braking.
Attempts by manufacturers to reduce front-end dive include the use of stiffer compression springs in the front forks. However, the user of stiffer springs has the unfortunate counter-effect of decreasing the capability of the front fork to dissipate smaller bumps during non-braking maneuvers. Manufacturers have also attempted to improve suspensions response by employing special coatings on a stanchion portion of each of the telescopic forks in order to reduce friction and thereby decouple the suspension system (i.e., compression springs) from the effects of road disturbances and braking of the motorcycle.
For example, certain manufacturers such as Bavarian Motor Works, Inc. (i.e., BMW) produce a line of motorcycles which employ an additional front suspension member commercially known as a Telelever™ which pivotally interconnects the lower (i.e., stationery) portion of each of the forks to the motorcycle frame as a means to prevent braking forces from traveling through the stanchion (i.e., moveable) portion of the telescopic forks. Instead, braking forces travel through the Telelever™ and thereby reduces compression of the front forks (i.e., front-end dive) that typically occurs during braking. However, the BMW Telelever™ system mounts and transfer loads to the upper portion of the frame and therefore fails to address other problems associated with conventional front fork suspension systems.
Such problems are related to front-end dive and include an increase in pressure at the contact patch of the front tire during braking which, in turn, increases the bending moment forces experienced at the steering head. The frame attach points of the steering head must have the capability to resist bending forces induced by the bending moments during braking. The need to resist bending results in an increase in the mass of the steering stem and its attach points. In addition, large braking forces transmitted through the contact patch at the front tire necessitate a generally stiff front axle to ensure that each of the telescopic forks compresses or collapses a relatively equal amount.
The ability of the front axle to resist uneven collapsing of the front forks is especially critical when the motorcycle is braking during a turn. Although a certain amount of weight transfer to the front end may be desirable in order to provide a desired amount of pressure on the front tire to temporarily increase the contact patch area and prevent front wheel sliding, an excess amount of front-end dive will result in reduced braking capability at the rear wheel to the extent that the overall braking performance of the motorcycle is adversely affected.
Another drawback associated with telescopic front forks is related to the high moment of inertia as a result of the large mass of the suspension and front wheel assembly rotating about the steering axis. The high moment of inertia can result in the development of a violent wobble at the front wheel at certain speeds. Although many manufacturers include a steering dampener to dampen oscillations occurring as a result of wobble, the added steering dampener unfortunately only further increases the weight and cost of the motorcycle.
Conventional telescopic forks also suffer from the inability to provide a manner for adjusting the spring rate of the compression springs to accommodate varying types of terrain, varying rider styles and varying riding conditions. Unlike conventional rear suspension systems for motorcycles which typically include an exterior mounted compression spring which is relatively accessible, compression springs of telescopic front forks are typically inaccessibly located inside the fork tubes and are not easily adjustable without completely disassembling the forks and completely removing the compression springs.
A further drawback of conventional telescopic front forks of motorcycles is associated with the angle at which the steering stem and forks are oriented relative to vertical and which is commonly referred to as the rake angle. In conventional motorcycles, the rake angle provides a self-steer effect with increasingly greater rake angles of the fork corresponding to a higher tendency of the motorcycle to self-steer which adds some measure of straight-line stability for the motorcycle and which can be advantageous at high speed. Unfortunately, road imperfections which induce off-centered upward forces on the front tire have a tendency to steer the wheel. For example, when encountering a longitudinal rut or groove in the riding surface parallel to the direction of movement of the motorcycle, a high rake angle also makes it difficult for the rider to steer the front wheel out of the rut. In addition, the self-steer effect also causes the motorcycle to drift toward a lower portion of the riding surface on crowned roads making it difficult to steer the motorcycle out of the lower portion.
The rake angle also increases the amount by which the rider must rotate the handlebars in order to effectuate a given amount of turning of the front wheel as compared to an arrangement where the forks are oriented perpendicularly relative to the riding surface. The perpendicular orientation of the forks would provide a one-to-one correspondence between rider input at the handlebars and steering output at the front wheel. A further problem associated with rake angle is related to the fact that during front-end dive, the telescopic forks collapse or effectively shorten, the wheel base (i.e., the distance between the front and rear wheels of the motorcycle) becomes proportionally shorter. Such reduced wheelbase unfortunately decreases the straight-line stability of the motorcycle.
An additional problem associated with rake angle of conventional front fork systems is a tendency of the rake angle to steepen or decrease during front-end dive which unfortunately causes a decrease in trail which is defined as the distance between the front tire contact patch and the point at which the front fork axes intersect the ground. A reduction in the trail as a result of front-end dive results in a decrease in the steering stability of the motorcycle. As is the case with the compression springs in the front forks, the amount of trail of the front wheel is typically preset by the manufacturer and is not easily modified to provide different handling characteristics as may be desired for varying riding conditions. Yet another drawback associated with rake angle is a the occurrence of a lowering of the motorcycle center of gravity in proportion to an increasing steering angle at the front wheel. When maneuvering a heavy motorcycle at slow speed, the lowering center of gravity means that the rider must use greater force at the handlebars in order to steer the motorcycle.
Telescopic fork systems suffer a further disadvantage which is related to the relatively large amount of suspension travel that is designed into the motorcycle in order to allow the front wheel to deflect sufficiently when encountering certain terrain conditions and obstacles. Generally, suspension travel can be defined as the distance over which the front wheel must be able to freely move without limitation in order to effectively absorb and dissipate bumps in the riding surface and accommodate the weight of rider and motorcycle. Unfortunately, the relatively large amount of front-end dive experienced by motorcycles equipped with conventional front forks necessitates a correspondingly large amount of front wheel travel which, in turn, increases the overall frontal area of the motorcycle and the attendant aerodynamic drag at speed.
In light of the above, the prior art includes several attempts to overcome deficiencies associated with steering of various vehicles and, more particularly, front wheel steering and suspension systems for motorcycles. For example, U.S. Pat. No. 364,335, issued to Burdess, discloses a velocipede such as a bicycle or a tricycle incorporating a steering mechanism for a front wheel mounted in a fork. The steering mechanism includes a plunger that compresses a spring contained within a cylinder when the wheel is turned such that the front wheel is biased toward its normal straight-line position in order to enhance stability of the velocipede.
U.S. Pat. No. 388,043, issued to House, discloses a velocipede or bicycle wherein opposing ends of the axle of the front wheel are connected to the bicycle frame by a pair of connecting rods. The connecting rods are constructed of bent form to provide room for turning of the wheel from left to right. The forks upon which the ends of the axle are mounted extend upwardly to a tiller or handlebars. A longitudinal slot is provided in the frame at the junction with the forks to provide adjustability with respect to the length of the connecting rods which connect the axle to the frame.
U.S. Pat. No. 431,061, issued to Kenney, discloses a velocipede having a steering wheel supported by a pivoted fork. The fork is connected with a cross bar or yoke having opposing ends which are connected by links to a similar cross bar which itself is connected to an upright shaft provided with a steering handle. Upon turning the steering handle, the front wheel is turned via the pair of links.
U.S. Pat. No. 477,583, issued to Van Bibber, discloses a bicycle having a front wheel supported by a fork which extends upwardly to a T-head having laterally projecting arms extending equally outwardly therefrom to form a transverse cross bar. The bicycle includes handlebars supported on a vertical member having a pair of laterally projecting arms of equal length forming a second transverse cross bar parallel with the transverse cross bar mounted above the forks. A pair of horizontal links are connected to the ends of each of the transverse cross bars such that turning motion of the handlebars is translated into turning motion of the forks for steering the bicycle.
U.S. Pat. No. 501,501, issued to Gehricke, discloses a child's cycle having a front steering wheel that is of small diameter to allow for the figure of a horse to be mounted thereabove. The front wheel is spaced forward of the rear wheel such that the legs of the user do not come into contact with the hind legs of the horse. A steering mechanism is provided to accommodate the forward placement of the front wheel and comprises a cross bar mounted above the fork which is connected by a pair of links to a corresponding cross bar connected to the handlebars by which the child's cycle may be turned.
U.S. Pat. No. 538,482, issued to Doan et al, discloses a tricycle supported by a front wheel. A front fork supports the front wheel and is pivoted in the frame of the tricycle. A cross-head mounted on top of the fork is connected to a steering lever by a pair of connecting links such that turning of the steering lever effectuates turning of the front wheel.
U.S. Pat. No. 1,175,744, issued to Giles, discloses a steering mechanism for cycles which comprises a mechanism that substitutes a steering wheel for conventional bicycle handlebars. The front wheel of the bicycle is supported by a fork having a laterally extending member mounted. The lateral extending member is connected at each of its opposing ends by a pair of links connected to opposing ends of a turning arm. The turning arm is connected to the steering wheel for guiding or directing the bicycle.
U.S. Pat. No. 1,262,625, issued to Berlin et al, discloses a steering device for a motorized plow wherein the front wheel is supported by a pair of forks having a transverse lever mounted on a forward end of the forks. An arm is positioned forward of the transverse lever in parallel relationship thereto. The transverse lever and arm are connected by a pair of links. The end of a steering shaft is pivotally mounted to a forward part of the arm such that when the steering shaft is turned left or right, the forks are turned enabling turning control of the motorized plow.
U.S. Pat. No. 1,623,726, issued to Herds, discloses a steering mechanism for a motor vehicle comprising a pair of horizontally oriented spring members extending from opposing sides of an axle of a front wheel of a vehicle. Opposing ends of the spring members are in turn connected to a pivotable casting. The casting is rigidly secured to a lower end of a vertically oriented pivot member. Rigidly secured to an upper end of the pivot member is a crank member which is secured to a rotatable steering shaft connected to the steering wheel of the vehicle. Turning of the steering wheel effectuates pivoting of the pivot shaft for controlling the directional movement of the front wheel.
U.S. Pat. No. 2,038,843, issued to Jones, discloses a three-wheeled automobile having two driving wheels in front and one steering wheel behind. The rear wheel is mounted on a rearwardly extending arm pivotally connected to a forwardly extending arm. The forwardly extending arm is mounted on an upright steering spindle whose vertical axis is located aft of the rotational axis of the rear wheel. A steering segment is fixed to the forwardly extending arm and has teeth which mesh with a steering worm gear connected to the steering wheel by means of a shaft to enable directional control of the aft steering wheel.
U.S. Pat. No. 2,199,966, issued to Timm, discloses a hydraulic actuator for a steering mechanism. A hydraulic actuator is connected to the wheel by means of a steering arm mounted atop a fork which has the wheel mounted therewithin. The fork is also connected to an equalization bar which is in turn connected to a control valve by a pair of links. The hydraulic actuator is specifically adapted to allow steering of the wheel at a pre-determined distance and rate best suited for the terrain and speed conditions.
U.S. Pat. No. 2,339,582, issued to Peterson, discloses a castor wheel such as may be used on agricultural machines. The castor wheel is mounted in a fork having an arm mounted on a pivot shaft attached to the fork. Cross links connect opposing ends of the arm to a pedal lever controlled by the operator. The castor wheel minimizes the tendency for the rear end of the machine to slip sideways down a hill or for the castor wheel to swing freely or wobble.
U.S. Pat. No. 2,510,798, issued to Cahill, discloses a single wheel steering mechanism wherein a wheel is carried by a vertically disposed fork mounted on the wheel axle having extending end portions. The opposing ends of the extended portions are, in turn, connected to a foot bar by a pair of connecting rods. The foot bar is in turn connected to a tiller or handle bar by a vertical shaft such that swinging the handlebars to the right or left effectuates a corresponding steering of the wheel.
U.S. Pat. No. 2,580,064, issued to Albright, discloses a fluid pressure-operated steering device wherein a pair of hydraulic motors are alternately operated in order to effectuate turning of a wheel mounted to a telescopic shock-absorbing landing gear. The steering device provides dampening of shimmying tendencies in order to eliminate tortional vibrations of the landing gear.
U.S. Pat. No. 3,110,352, issued to McClamon, discloses a wheeled vehicle steering device wherein wheels on forward and aft ends of the vehicle are cooperatively interconnected such that the wheels are turned in opposite directions to allow for very small turning radii. The steering of the forward and aft wheels is effectuated by handlebars actuating a steering post connected with the wheel steering unit by a set of linkages. One of the wheels of the vehicle is a freely castoring front wheel which swings to a complementary position dependent upon the turning radius.
U.S. Pat. No. 3,521,904, issued to Sheffer, discloses a vehicle structure having a front wheel that is steerable by pivotal movement of a handlebar unit connected to a connector bar. A pair of links attached to opposing ends of the connector bar are pivotally attached to a yoke or fork straddling the front wheel. The yoke and, hence, the wheel structure are pivotally moved in response to pivotal movement of the handlebar unit for steering the vehicle structure.
U.S. Pat. No. 4,353,567, issued to Weldy, discloses a steering and suspension system for a front wheel of a three-wheeled vehicle. The steering system includes a pair of suspension frames that pivotally support the front wheel. A pair of steering arms are pivotally connected to the suspension frames at one end thereof. An opposite end of each of the steering arms is pivotally connected to the vehicle's front cross frame member. Each steering arm moves in an arcuate path in response to a linkage that is actuated by a driver in a manner causing one steering arm to pivot inwardly in a direction opposite to the direction of desired turn of the wheel while the other steering arm pivots outwardly in such a manner that the wheel is leaned into the turn.
U.S. Pat. No. 4,685,694, issued to Kouyama, discloses a steering apparatus including an angle-increasing-mechanism allowing for large steering angles to be imparted to the steering wheel in response to small pivotal angles of the handlebars. The handlebars are pivotally connected to a top plate located forward of the handlebars and interconnected by a pair of connecting rods. The distance from the handlebar pivot to the connecting rod at one end is greater than the distance of the top plate pivot to the connecting rod at the opposing end. This difference results in an increasingly large pivot angle of the top plate with respect to that of the handlebars to thereby form the angle-increasing-mechanism allowing relatively sharp radius turns with smaller angular input at the handlebars.
U.S. Pat. No. 4,773,499, issued to Frye, discloses a steering mechanism having a forkless steerable wheel and axle structure having a hydrostatic motor integrated therewithin. The axle structure is steerable by means of a pair of left and right actuators that cooperate to effectuate steering of the wheel. More specifically, a piston rod of one of the actuators is extended while the opposing piston rod of the remaining actuator is retracted causing the center of the wheel to shift to the right or left depending upon the direction of steering.
U.S. Pat. No. 5,820,439, issued to Hair, III, discloses a gyro-stabilized remote controlled toy motorcycle having a front wheel that is supported for rotation on a fork that is coupled to a steering post. The steering post is inclined aftwardly with its axis passing through the axis of the front wheel to provide a castor effect which tends to turn the front wheel toward the direction in which the motorcycle is leaning which thereby biases the motorcycle toward an upright position when in motion.
U.S. Pat. No. 6,120,048, issued to Li, discloses an auxiliary steering device such as for a tricycle which provides secondary steering in addition to the handlebars. The secondary steering device is connected to the handlebars by two connection rods to enable an adult to manipulate the steering of the handlebars from behind the tricycle.
U.S. Pat. No. 6,786,796, issued to Suto, discloses a radio controlled two-wheeled vehicle toy including a main body having a front fork that is rotatably mounted on the main body. A front wheel mounted to the front fork may be directionally controlled by a steering control portion mounted on a front side of the main body.
U.S. Application No. 2006/0037797 and U.S. Application No. 2006/0037799, filed by Mathon, disclose a motorcycle having a dual beam chassis and a steering mechanism comprising a handlebar linkage controlling a front wheel mounted to the motorcycle. The steering linkage is located inside a tubular front fender housing and comprises a steering shaft extending through a fixed tube and which is coupled to a rotatable tube upon which the wheel is mounted. The steering shaft is driven by an angular mitre gear engaged to an identical gear driven by the steering linkage. A four-bar-linkage disposed adjacent the handlebar communicates angular motion to drive the mitre gear which, in turn, engages the steering shaft to provide directional control of the front wheel.
U.S. Pat. No. 4,265,329, issued to de Cortanze, discloses a frameless motorcycle having a steering mechanism comprises of a handlebar rotatably mounted to a motor of the motorcycle. A control rod extends from the handlebars to a pivoting bracket which, in turn, is connected at an opposite end to a rotatable triangular element mounted on a swing arm extending in a forward direction of the motorcycle. The front wheel is mounted on a swing arm in such a manner that the triangular element which is linked to the handlebars may pivot about an inclined axis in order to effectuate directional control of the front wheel of the motorcycle.
U.S. Pat. No. 4,526,249, issued to Parker, discloses a front suspension system for a motorcycle comprising a pair of upper and lower control arms extending forwardly from the body of the motorcycle. Each of the control arms is connected to a kingpin extending downwardly along one side of the front wheel. The upper end of the king pin is connected to a steering shaft that in turn is connected to the handlebars of the motorcycle such that turning of the handlebars causes the king pin to pivot about the forward end of the lower control arm to effectuate directional control of the front wheel during steering.
U.S. Pat. No. 4,702,238, issued to Trema, discloses a suspension device for a motorcycle wherein the front and rear suspension systems are coupled in a manner which facilitates control of the suspension-shock absorber interaction. The front wheel steering-suspension system comprises an upper arm disposed parallel to a lower arm each hinged to the front chasse and cooperating to support the front wheel. A pivot support is mounted on a forward end of the lower arm and is connected by a rod to the steering handlebars to facilitate directional control of the front wheel.
U.S. Pat. No. 4,741,545 issued to Honma, discloses a front wheel steering device for a motorcycle comprising upper and lower swing arms having their rear ends pivotally joined to the engine case. The front wheel is steerably supported by a knuckle to which an axle of the front wheel is mounted. The forward ends of the upper and lower swing arms are pivotally connected to the knuckle member. The knuckle is angularly moveable for steering the front wheel via the handlebars.
U.S. Pat. No. 4,890,857 issued to de Cortanze, discloses a steerable wheel mechanism for land vehicles having a steering mechanism that is similar to that described above for the de Cortanze '329 reference.
U.S. Pat. No. 5,133,223, issued to Morri, discloses a device for steering a front wheel of a motorcycle and which comprises at least one arm pivotally anchored at its rearward position to the motorcycle frame. The rim of the front wheel is supported by an outer hub within which is coaxially disposed an inner hub. The inner hub is pivotally mounted on a steering pivot which, in turn, is fixedly secured to an axle extending from the forward end of the support arm. A lever is rigidly mounted to the inner hub and is connected to the handlebars by means of a control rod in order to effectuate directional control of the front wheel by pivotal movement thereof about the pivot.
U.S. Pat. No. 5,361,864, issued to Tanaka and U.S. Pat. No. 5,782,313, issued to Kurawaki et al disclose a front wheel swing arm type steering and suspension system for a motorcycle which is constructed similar to the arrangement described above for the Honma '545 and Parker '249 references.
U.S. Pat. No. 3,539,196, issued to Fleming, discloses a vehicle steering assembly for controlling a steerable wheel. The wheel is rotatably mounted on an axle member having opposed ends each of which is connected to supporting struts. The struts extend aftwardly and are pivotally connected at fixed pivot points to a frame of the motorcycle in spaced relation to one another. The strut together with the axle member and the spaced pivot points form a closed four-bar-mechanism in the form of an isosceles trapezoid. The vehicle is steered by pivoting the strut members such that the axle and, hence, the wheel are simultaneously rotated and laterally translated with respect to the vehicle.
U.S. Pat. No. 6,095,891, issued to Hoeting and U.S. Application No. 2006/0009119, filed by Hoeting, disclose a remote control toy vehicle comprising a four-bar-mechanism connecting a front castoring wheel to a chassis of a motorcycle. The front wheel of the motorcycle is mounted on a pair of telescoping front forks extending upwardly to the four-bar-mechanism. The four-bar-mechanism is comprised of left and right spaced members, a fork coupler and a front end frame. The fork coupler is connected to the front fork. The toy vehicle includes a link which is operatively connected to a steering drive and to the four-bar-mechanism on the opposite end in order to deliver steering outputs to the front fork to impart left or right pivoting motion to the front wheel.
Although some of the above-referenced patents disclose steering mechanisms and suspension systems for overcoming certain deficiencies associated with telescopic front forks such as front-end dive, none of the references are understood to disclose an arrangement wherein all of the above-referenced drawbacks associated with telescopic forks are addressed. More specifically, none of the above-mentioned references are understood to disclose a wheel steering and suspension system of reduced overall mass and which allows for a relatively lower center of gravity and improved handling of a motorcycle.
As can be seen, there exists a need in the art for a steering mechanism for a vehicle such as a motorcycle which minimizes or eliminates the problems associated with front-end dive during heavy braking. Furthermore, there exists a need in the art for a steering mechanism for a vehicle which provides a means for improved suspension and handling performance during braking. More specifically, there exists a need in the art for a steering mechanism and suspension system for a motorcycle with improved handling in response to longitudinal ruts or grooves in the road surface over which the motorcycle may be traveling. Additionally, there exists a need in the art for an improved steering mechanism which reduces steering input at the handlebars in order to achieve a given turning radius as compared to the steering input required in conventional telescopic fork suspension systems.
Additionally, there exists a need in the art for a steering mechanism and suspension system for a motorcycle that minimizes shortening of the wheel base and trail throughout the range of suspension travel. Also, there exists a need in the art for a steering mechanism and suspension system for a motorcycle which allows for installation and removal of the front wheel from a single side of the motorcycle without the need to remove other hardware such as the brake components. Finally, there exists a need in the art for a steering mechanism and suspension system for a motorcycle which is of light weight and low cost and which lowers the overall center of gravity of the motorcycle as compared to motorcycles having conventional telescopic front fork systems.